1. Field
The present technique relates to a storage device, a control device, and a vibration-detection method that are configured to protect an adjacent track of a magnetic disk from data writing which occurs due to vibrations created by an actuator.
2. Description of the Related Art
A magnetic-storage device writes data onto and read data from a magnetic disk by using a magnetic head.
Then, the magnetic head should be positioned on a predetermined track provided on the magnetic disk, so as to write data onto and read data from the magnetic disk. Therefore, servo information is recorded in advance in a servo sector provided between data sectors provided on the track by using a servo-track writer or the like. When writing data onto and reading data from the magnetic disk, the magnetic head is moved to the position of a target track based on information about the current position. Next, the magnetic head is positioned on the target track based on information about the servo sector, the information being read by the magnetic head. After that, feedback control is performed so that the magnetic head is positioned at the center of the track while data is written onto or read from the data sector.
Thus, the magnetic head is subjected to the positioning control. When the amount of off-tracks detected by reading the servo information exceeds a threshold value, the magnetic head usually stops performing the write operation. However, since the servo information is a discrete signal obtained for each of servo sectors, it is difficult to detect the off-track amount when the magnetic head exists between the servo sectors, that is to say, when the magnetic head is positioned in the data sector. Therefore, methods performed by using a sensor signal have been proposed. For example, according to a method disclosed in WO97/27588, an accelerometer is installed on a magnetic head and/or a carriage supporting the magnetic head, and a signal transmitted from the accelerometer is fed back so that the magnetic head is positioned.
According to the above-described method disclosed in WO97/27588, a sensor is installed on the magnetic head and/or the carriage, and the sensor signal is fed back so that the magnetic head is positioned. In actuality, however, it is difficult to position the magnetic head by using the signal of the sensor alone. Therefore, control is usually performed so that a correct off-track amount is detected by reading a servo signal and the magnetic head is positioned on a target track.
However, if the component of a residual vibration created by head positioning is an integral multiple of a Nyquist frequency which is a half of a sampling frequency of the servo sector, for example, when the magnetic head is positioned on the target track by performing seek control, the magnetic head may be off the track in the data sector even though the magnetic head is on the target track in the servo sector, and there is no means configured to detect the off-track occurring in the data sector when the magnetic head is in the above-described vibration state. Namely, when trying to detect the off-track amount by using the servo signal at the time where the magnetic head vibrates with a frequency component which is an integral multiple of the Nyquist frequency, it is difficult to detect an actual off-track amount. This is because the vibration cycle of the magnetic head is synchronized with a cycle in which the servo sector passes the magnetic head 2.
Further, according to another method, a shock sensor is used for an external shock so that operations are stopped when the shock is exerted. However, a vibration which will be discussed is a small residual vibration which occurs immediately after the magnetic head is positioned on the target track by performing the seek control. Since an ordinary shock sensor is configured to detect a vibration with a large amplitude, it is basically difficult for the ordinary shock sensor to detect the small residual vibration. Further, even though the sensitivity of the shock sensor is simply increased, so as to detect the small residual vibration, a small external vibration and/or an insignificant residual vibration is erroneously detected, as an off-track, so that the write operation is stopped frequently. Subsequently, the performance of the magnetic head is significantly decreased.
Further, the off-track margin becomes increasingly smaller as the density of track pitches of the magnetic disk becomes increasingly higher, which makes it difficult to ignore any vibration irrespective of how small it is.